This invention relates to an imaging apparatus for non-destructively determining the density distribution, relaxation time distribution or the like, of nuclear spin inside an object to be inspected by use of nuclear magnetic resonance (NMR). More particularly, the present invention relates to an imaging apparatus using nuclear magnetic resonance which apparatus has especially improved spatial resolution.
X-ray CT (computed tomography) and ultrasonic imaging apparatuses have gained conventionally a wide application as apparatuses for non-destructively inspecting the internal structure of a human body or the like. Recently, attempts to carry out the similar inspection by use of nuclear magnetic resonance have proved successful and it has been clarified that this NMR technique provides the data that can not be obtained by the X-ray CT and the ultrasonic imaging apparatuses.
Imaging apparatuses using nuclear magnetic resonance determine non-destructively data relating nuclear magnetic resonance such as the density distribution and relaxation time distribution of the nuclear spin inside the object to be inspected from outside the object, and reconstructs and produces the cross section of a desired measuring target of the object in the same way as in the X-ray CT.
Various methods have been proposed in the past to detect various NMR data such as the density distribution and relaxation time distribution of the nuclear spin in the imaging apparatuses using nuclear magnetic resonance. With the exception of a magnetic focusing method, most of these methods place the nuclear spin to be discriminated in a specific static magnetic field by use of linear gradient magnetic fields that are perpendicular to each other, and put the coordinates to the nuclear spin. In this case, the resonant frequency of the nuclear spin is determined by the sum of the intensity of the linear gradient magnetic fields and the static magnetic field and hence, the spin position can be detected by analyzing the nuclear signal.
In the imaging apparatuses that have been proposed to date, it has not been attempted to apply the linear gradient magnetic field having the intensity corresponding to the size of the object to be inspected or the size of an inspection zone.
For this reason, if the object to be inspected is a human body, for example, the spatial resolution in the case of inspection of the head becomes the same as the spatial inspection of the bust. If the object to be inspected is small such as the head, the number of elements for reconstructing the image representative of the head becomes small and the image becomes more rough in comparison with the bust.